Introduction: How to Make a Very Simple Savonius Wind Turbine
The influence that more and more Wind Turbines have on World Energy Production is indisputable. It is very common to explore these types of devices during class time when learning about Science, Technology, Engineering and Mathematics (STEM). While using these learning tools, you offer to your students wider possibilities of acquiring knowledge and skills in these subjects while exploring, designing and manipulating small models of them. These projects are also beneficial for teachers since they provide interesting and entertained opportunities to integrate theory with practice while motivating the students and supporting the teaching learning process.
In my experience, it is common to see students experiment with small electric motors to which small propellers are attached. The propellers along with the motors are able to generate an electric current while interacting with the wind. Along with it, they manage to turn LEDs on and make small electrical devices work. There is a lot of knowledge behind these experiments and it is fascinating to see the expected results.
It is important to note that the Horizontal Axis Wind Turbines (HAWT), like the one in the previous example, are not the only ones who may generate this current. That is why in certain cases other types are usually used, such as the Vertical Axis Wind Turbines (VAWT), where the Savonius type stands out. In my case, I think it is also important to deal with this type of Wind Turbines in classes in order to stretch the students’ understanding.
In this Instructable I offer the steps that I followed for the construction of a VAWT (Savonius). I did my best to make it easy to replicate as I believe it is worth experimenting with it in a classroom environment. Bearing this in mind, the materials and tools that were considered for the construction of the model are cheap and likely to be accessible.
With these steps and the guidance of a teacher, students will be able to build and explore the mechanical principles and engineering of a common type of VAWT. They should also be able to apply and understand certain physics principles and mathematical knowledge, such as: Drag, Friction, Torque, Electromagnetic Induction, Center of Mass and balance, Gravity Force, Direct Current, the Determination of Planes by three or more points, certain Geometric Figures, among others.
Another important aspect is the fact that they will be able to relate the model’s construction with Renewable Energy Sources and address the importance that this entails for the Sustainability of life in our Planet.
Although I am presenting how I made the Cardboard and Pencils Version, I offer all the CAD files including STL and DXF for those who prefer and find it convenient other construction methods such as: 3D printing, CNC cutting, laser etc. ... Also for those who prefer to transform, adapt, scale, etc. ... my design, I included a STEP file of the entire assembly. If you want another type of file or need my help, do not hesitate to contact me.
I did this project together with my 10 year old son. We both really enjoyed its construction!
--- Printed templates
--- Three toilet paper rolls
--- Small electric motor (3-6V DC)
--- Pair of compasses
--- Soldering iron and solder (Optional)
--- Paper Glue
--- Hot Silicone Gun
--- Hair dryer, fan or similar for experiments
Step 1: DESIGN CONSIDERATIONS
This is not the first VAWT I have built, in this link (https://www.instructables.com/Portable-Savonius-Wind-Turbine-With-Deflectors/) I attached a previous one that I also published earlier. Since this version has been designed specifically for the school environment, to be ensemble with the students as part of a class project, I considered the use of highly accessible materials. Among the materials that I initially considered were pencils, cardboard, and erasers.
The graphite in pencils is used as a lubricant in locks, I have use it before and it works. I asked myself if I could use it as a substitute for ball bearings so as to simplify the model construction and I think it has been a total success. For this Savonius Wind Turbine, I decided not to use ball bearings in order to facilitate its construction. In contrast, a pencil is used.
Most of the frame is made of 4mm thick cardboard. At first, I had my doubts if it would be effective. Since this material is much more flexible than plastics, for example, it was necessary to create the cardboard structure to accommodate 3 piles of pencils to avoid any instability. During this part of the modelling, students should be exposed to the material selection. It is impressive to see how they may be able to reach to interesting and deep conclusions by themselves while finding the best solutions no matter how old they may be.
In the prototype that I am presenting below, no special attention was paid to ensuring that the base discs were perfectly vertical with respect to the central axis (pencil), trying to recreate an expected result after the construction process by the students. In this version of pencil and cardboard, some kind of suspension had to be created so that the motor could adapt to the vertical changes of position of these discs while they rotated. These position changes are detrimental to electrical generation, since if the wheel coupled to the motor shaft (generator) is not in continuous contact with the Savonius rotor, the LEDs will not be able to turn on. At first, I considered using springs, rubber bands, and even sponges placed under the electrical motor. After thinking a bit and maybe while taking advantage of this experiment moment to elicit from your students’ previous knowledge, I decided to use the Force of Gravity. I placed the motor on the edge with a tendency to fall backwards. Though the eraser that is fixed to the shaft of this motor collides with the lower surface of the Savonius rotor, the assembly does not fall backwards. However, it is able to adapt to its position variations while rotating.
One aspect that I have found that can cause certain problems in the generation of this type of simple Wind Turbines is the direct coupling of the motor shaft to the Savonius Rotor shaft. The RPM obtained with this method are low, which in certain cases cannot obtain a minimum voltage and power value in order to turn on the LEDs. The use of multiplier mechanisms such as pulleys or gears is usually convenient in these cases, but it also complicates the construction. The solution I propose solves this problem while simplifying this entire process.
The erasers that are included in the pile pencils were used at the base of the whole assembly to avoid slipping and they worked very well.
The dimensions of this Wind Turbine are rather small and are conditioned by the dimensions of the materials that were used. Specifically, the length of the pencils, the length of the cardboard cylinders and the dimensions of the sheets where the templates are printed, avoiding complications and making their construction as easy as possible. With these conditions and due to its dimensions, the torque obtained is relatively low, which is why relatively high wind speeds are required. If you use a hair dryer or similar it will work without problems even on the lowest speed selection. In an outdoor environment the wind will have to be strong for it to turn on the LEDs. If you want more torque, I suggest tying two pencils on each pile and using taller half-cylinders, perhaps like the ones on the Pringles Can.
I recommend that the teacher should first build a first model version and anticipate the possible complications that the students may encounter. Depending on the available time, students’ background information and age, 2 or 3 sessions may be used for the construction and analysis of this Project.
Step 2: THE TEMPLATES
To obtain the Templates it is first necessary to print them on paper. I included a PDF document with the templates. After printing them you will have to cut the figures with a scissors along the contour line. Using the paper glue, glue them to a base cardboard and again cut out the excess parts.
It can be difficult to cut the cardboard if the scissors are very small. Using larger scissors like this can be convenient.
Step 3: OBTAIN THE SAVONIUS ROTOR BLADES AND GLUE THEM TO THE BASE DISK
Overlap the cardboard cylinders over the base circle marks and with a permanent marker make a mark of the middle of each cylinder. With a pair of scissors, cut vertically upward from each mark to the other end. You should get 5 semi-cylinders that will make up the blades of the Savonius Rotor. Using some glue, glue them on each mark. The glue should be strong. In my case I used Super Glue but the hot silicone should work without any problems. In any case, the teacher must be very attentive in this step when the students carry out this operation. Wearing protective glasses is recommended.
Step 4: POSITIONING THE CENTER AXIS (PENCIL)
First, you will need to sharpen the pencil at each end. Verify that the pencil is of HB or similar denomination. This will ensure that tip is hard and lasts for a long time before readjusting and / or re-sharpening the pencil.
The story behind making something as simple as a pencil is amazing. I recommend you consult with your students their history here or indicate their study.
With the tip of the scissors, pierce the center mark of the base disk and insert the pointed pencil. Try to make it fit more tightly. Don't paste it yet.
Step 5: POSITIONING THE UPPER DISC AND FIXING THE CENTRAL AXLE
Before you can place the upper disc in its position, you will have to pierce its central mark also with the help of the tip of the scissors. Then, insert the disc and verify that the blades are aligned and touching their marks. Using glue, fix them in position. Insert the center axle (pencil) a little further, leaving a reasonable slack to fit the wheel and generator at the bottom. With more glue, fix the pencil to the two base discs.
Step 6: PREPARING THE STAND BASES
Since these bases are also made of cardboard and to prevent the tips of the shaft pencil from snapping on them, two small squares of thin aluminum sheet were placed. In my case, I took advantage of the used instant glue containers. With scissors I cut out these pieces and later glued them on top of the central marks. With the help of a pen I made some indentations where the tips of the pencils would be contained. The coefficient of friction between the tip of the pencil and these plates is low, something very favorable. Since these plates are also smooth and the rotor mass is low, the wear on the tips is also minimal. Later I inserted the piles (pencils) in the base, letting their erasers protrude at the bottom. Try that all the erasers of these pencils are level. With glue, fix these pencils to the bottom base.
Step 7: COUPLING THE SAVONIUS ROTOR TO THE BASES
Place the upper base, it should be tight and you should not glue it. Insert the Rotor making sure that the tips of the pencils are lodged in the grooves of the center plates. Fit the entire assembly by sliding the top base down or up. Check that when you blow it the Rotor turns freely
Step 8: PREPARING THE FINAL ASSEMBLY
To create the wheel that will be placed on the motor (generator) an eraser was used. First, its center is determined. Using a compass or a coin a circular mark is made. With a scissors it is cut until it takes a circular shape. The shape is perfected with sandpaper.
Another way to carry out this operation would be by making the cut itself with the help of the compass as seen in the image.
The circular eraser is inserted into the generator shaft and glued to it. Try not to allow glue to get inside the motor, which would cause a jam. The eraser should only be in contact with the shaft and not with any other surface of the motor.
If the motor is brand new, it should have its terminals with holes. If you insert the tips of the LED legs and join them mechanically by bending them, you may avoid having to use the soldering iron and solder. Note the polarity of the LED and the polarity that appears on the generator terminals when it rotates should match.
Pieces of cardboard are glued to the base of the generator until the necessary height is reached so that the wheel of the generator makes contact with the lower part of the base disc of the Savonius Rotor. A little glue is placed on the central part of these cards and it is attached to the edge of the base where it will be held. The motor must pivot and adapt to the possible position variations of the Savonius Rotor base disc when it rotates.
Nothing else, you are ready! I am looking forward to hearing from your experiences while using this model in your classrooms. I am sure the students will learn the different theories while enjoying!
I hope you find it useful.
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